Abstract PLC programmable controller: PLC English full title Programmable Logic Controller, Chinese full title as the programmable logical controller, the definition is: One kind of digital operation operation's electronic system, for designs specially in the industry environment application. It uses a kind of programmable memory, uses in its internally stored program, the actuating logic operation, the sequential control, fixed time, counting and arithmetic operation and so on face user's instruction, and through digital either simulation type input/output control each type machinery or production process. PLC is based on the electronic accounting machine, and is suitable for the industry field work electric controller. It stems from following the electricity control device, but it does not look like following the electricity installs such, realizes the control through electric circuit's physical process, but mainly saves depending on the movement in the PLC memory the procedure, carries on into the information conversion to realize the control. Enters the information conversion, the reliable physics to realize, may say that is PLC realizes the control two essential points. Enters the information conversion to save depending on the movement in the PLC memory the procedure realizes. The PLC procedure both has the Manufacturer system program (not to be possible change), and has the application which the user develops voluntarily (user) the procedure. The system program provides the movement platform, simultaneously, but is also the PLC procedure reliability service and the signal and the information transformation carries on essential public processing. The user program according to controls the request design by the user. What control request, should have what user program.
The reliable physics realizes mainly depending on loses the human (INPUT) and the output (OUTPUT) the electric circuit. The PLC I/O electric circuit, is designs specially. The input circuit must carry on the filter to the input signal, removes the high frequency interference. Moreover is isolates with the internal computer electric circuit on the electricity, depending on light pair part establish contact. Inside and outside the output circuit is also the electricity isolation, depending on light pair part or output relay establish contact. The output circuits must carry on the power amplification, by drives the general industrial control primary device sufficiently, like solenoid valve, contact device and so on. The I/O electric circuit is many, each entrance point either output must have one I or the O electric circuit. PLC has multi-I/O to use the spot, generally also has how many I/O to use the electric circuit. But because they are composed highly by the integrated electric circuit, therefore, accounts for the volume not to be big. The input circuit time monitors is inputting the condition, and its interim in input temporary storage device. Each entrance point has a corresponding memory its information temporary storage device.
The output circuit must output latch's information transmission for the output spot. Outputs the latch and output is also 11 correspondences. Here input temporary storage device and the output latch are actually PLC the processor I/O mouth register. They with the computer memory exchange information through the computer main line, and mainly realize by the run-time system procedure. Loses the person temporary storage device's information to read PLC in the memory, calls input refurbishing. In PLC has specially the opening depositing infed information mapping area. This area's each corresponding position (bit) called it inputs the relay, or calls the soft contact. These positions become 1, indicates the contact to pass, sets 0 breaks for the contact. Because its condition is obtains by input refurbishing, therefore, it reflects is the input state.
Key words: programmable logic controller (PLC); industrial washing machine; Control
